In democracies, individual decisions about voluntary giving and voting determine the type and amount of public goods. Understanding the neural processes that determine these public-good decisions is important for distinguishing between economic theories, which in turn can inform public policy. Recent neuroeconomic work has provided initial evidence that charitable giving may be driven by both "pure altruism" from experiencing increases to the public good regardless of their cause (Harbaugh, Mayr, &Burghart, under review), and "warm glow" from the agency effect of having chosen to give (Moll et la., 2006). This work has also shown that both activity in neural reward centers and in prefrontal regions independently predicts rates of giving to a charity. However, these results come from experiments with predominantly young adults. In practice, the level and type of public goods are determined by the decisions of older adults, who give more and vote more often than the young do. At the same time, there are known neuro-cognitive changes that occur with age that might affect economic decisions. Therefore, our first specific aim is to generalize and extend the existing results on the neural basis of public-good decisions across a large sample of young (age 25-35, n=50) and older adults (age 65- 75, n=50). The experimental protocol will include (a) a condition in which the subjects'payoff and the funding for a public good change in a mandatory, tax-like manner, (b) a voluntary-giving condition where people can accept transfers or not, and (c) a voting condition where majority rule among a group of participants determines if taxes will be levied on all and transferred to the charity. By considering both taxation and contributions from older segments of the society, this design covers the most critical sources of funding for public good. Our second specific aim is to test hypotheses about how neural and psychological changes across the life span translate into age-related changes in public-good decisions. For example, we predict that age-related decline in the ability to represent long-term goals in prefrontal cortex reduces the tendency to voluntarily provide or vote for public goods. However, age-related increases in warm- glow should exert an opposing positive effect on charitable-giving, but not on voting for taxation since, which provides less opportunity for warm glow. In our preliminary work, we also found that the mere opportunity of free choice triggered reward-center responses, but also "neural costs" in terms of substantial prefrontal activity. Given that prefrontal activity should be particularly demanding for old adults, we predict a reduction of the free-choice benefit in old adults, a result with potentially important consequences for comparing welfare benefits of taxation and giving across age groups. In preliminary work on young adults using economic experiments and fMRI scanning we have shown that it is possible to use neural activation in reward centers as a measure of the marginal rate of substitution between payoffs to oneself and to a charity, and that this measure predicts voluntary giving decisions. We propose to apply similar methods to a population of older subjects, and to both charitable giving and voting experiments. The objective is to see if economic models can explain these behaviors in the age groups that are most likely to give and to vote, and to see how age related changes in the brain are related to the observed changes in voting and charitable giving that occur with age.